(1) Field of the Invention
The present invention relates to a color image forming apparatus comprising: a plurality of image supports on which toner images are formed; a plurality of transfer means arranged in series so as to be opposed to the corresponding. image supports and causing the toner images to transfer to a print medium; an endless dielectric belt running continuously and disposed between the toner supports and the transfer means; a charging means disposed upstream of the multiple transfer means for causing the dielectric belt to electrostatically attract print media thereto; and charge erasing and cleaning means disposed upstream of the charging means for erasing the charge on the dielectric belt and cleaning the leftover toner, wherein a plurality of toner images formed on the respective multiple toner supports are successively transferred to the conveyed print medium by the respective transfer means to form a color image.
(2) Description of the Prior Art
A conventional color image forming apparatus, as disclosed in Japanese Patent Application Laid-Open Hei 9 No.22,158, includes: multiple image forming portions each having a drum-type image support; transfer chargers successively transferring the images formed in the image forming portions to a single print medium which is conveyed by a transfer belt; and a suspending means for suspending the transfer belt in such a manner that the transfer belt is curved upwards toward the downstream side with respect to the conveyed direction of the print media or in the direction matching the rotation of the image supports, and the contact area between the image support and the print medium becomes greater as the print medium is conveyed from one image forming portion to the next.
Japanese Patent Application Laid-Open Hei 9 No.50,197, discloses a configuration in which a plurality of transfer rollers are arranged opposing respective photoreceptor drums with a conveyer belt held in between. In this configuration, each transfer roller is applied with a voltage from a common transfer voltage applying unit and is abutted against the conveyer belt with a predetermined nip width while their resistance is adjusted so that it decreases with respect to the order in which the associated photoreceptor drums are laid out.
In accordance with Japanese Patent Application Laid-Open Hei 9 No.22,158 and Japanese Patent Application Laid-Open Hei 9 No.50,197, both configurations need separate power sources: one as the transfer power source for applying a voltage to the transfer chargers or transfer rollers as the transfer means for transferring the toner image to print media; and one as the power source for applying a voltage to the transfer belt or the conveyer belt so as to electrostatically attract print media thereto. Therefore, these configurations needed many parts and hence became bulky and high in cost.